So we started to check all of the usual suspects such as NIC and DNS issues.
In my experience, in a system that has the interconnect tuned well and not a ton of cross instance traffic, these should be in the 5ms or less range. In this case, while performing a healthcheck on a system we immediately noticed an issue with the interconnect manifesting itself in AWR as long ping times between nodes as seen in dba_hist_interconnect_pings: If there are not enough ports available for the needed interconnect traffic, interconnect latency can occur. Since interconnect traffic is usually short lived and frequent, there need to be enough ports available to ensure timely communication. What that means is, when a client initiates a request it choose a random port from ephemeral port range and it expects the response at that port only.
Oracle RAC interconnect traffic specifically utilizes the User Datagram Protocol (UDP) as the port assignment for the client end of a client-server communication to a well-known port on a server. Simply explained, ephemeral ports are the short-lived transport protocol ports for Internet Protocol (IP) communications. But what are they and why are they important? For purposes of this post I won’t deal with excessive interconnect traffic, but instead I will deal with latency caused by the lack of ephemeral ports. As a matter of fact, it’s part of the prerequisite checks for RAC installation. Why not?“, ensuring that there are enough Ephemeral Ports for Interconnect Traffic is important. Building upon my previous post “ Ulimit nofiles Unlimited.
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